Astronomers have employed the visual acuity of the European Southern Observatory’s Very Large Telescope (VLT) to capture these incredible images of the changing surface of red supergiant Betelgeuse. The star is currently experiencing a period of yet-to-be explained dimming that has taken it out of the top 20 brightest stars in our sky.
Betelgeuse, like many supergiant stars, is a dynamic object with a changing luminosity. But its dimming, now at 36 percent of its average brightness, is unprecedented. A team of astronomers from KU Leuven in Belgium have been studying this dimming event in detail since December 2019, capturing a stunning new image of the star's surface using the VLT'S SPHERE instrument. As luck would have it, they had also observed the supergiant in January 2019, giving us incredible before and after photos of the dimming star.
Red supergiant stars are a lot more massive than our Sun and mind-bogglingly larger, extending hundreds of millions of kilometers into space, compared to the 1.4 million kilometers (865,370 miles) of our own Sun. For this reason, these stars have very low densities, so internal processes can create peculiar shapes. The two new images show how Betelgeuse is changing shape rather than appearing spherical, which you'd expect from a star.
Researchers trying to understand the cause of the unusual dimming have two main hypotheses.
“The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us,” team leader Dr Miguel Montargès said in a statement. “Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen.”
The VLT is key to the efforts to understanding Betelgeuse. SPHERE is one of the few instruments capable of imaging the star. However, a different team led by Pierre Kervella from the Observatory of Paris used the VLT's VISIR instrument to capture another image in December that shows the dust released by the star. That tiny orange dot in the middle is the new image of the surface of the star taken by SPHERE.
“The phrase ‘we are all made of stardust’ is one we hear a lot in popular astronomy, but where exactly does this dust come from?” said Emily Cannon, a PhD student at KU Leuven working with SPHERE images of red supergiants. “Over their lifetimes, red supergiants like Betelgeuse create and eject vast amounts of material even before they explode as supernovae. Modern technology has enabled us to study these objects, hundreds of light-years away, in unprecedented detail giving us the opportunity to unravel the mystery of what triggers their mass loss.”
The teams will continue to monitor this fascinating object and thanks to this strange dimming event, soon we will know more about red supergiants than ever before.